January-February 2011

Weather Front

by Kimbra Cutlip

Meteorology From the Moon

In yet another confirmation of the wisdom of oral traditions, researchers have found truth in folklore associating moon phase with rainfall. Societies as disparate as Zuni Indians and Medieval Germanic tribes had names for various states of the moon that foretold the weather.

A team of researchers decided to revisit the subject after finding a link between moon phase and stream runoff. Their curiosity led them to review 100 years of data from nearly 11,000 U.S. Geological Survey stations across the United States. They discovered a slight increase in stream flow around the quarter moon, halfway between the full and new moons. To confirm a link to rainfall and not to the tides, the researchers turned to the U.S. Historical Climatology Network, a database with daily precipitation information for more than 1,200 stations from as early as 1895.

They concluded that precipitation tended to rise a few days before the quarter moon. While the effect is small, accounting for a 1 to 2 percent change in rainfall or stream runoff, it is a real effect.

The work—conducted by Arizona State University Professor (and Weatherwise contributing editor) Randy Cerveny, Ph.D. student Bohumil Svom, and Russell Vose of NOAA—appears in Geophysical Research Letters.

KIMBRA CUTLIP is a freelance writer and former assistant editor for Weatherwise.